The present invention relates to a hub assembly in a disc drive. More particularly, the present invention relates to a disc spacer for supporting a disc on a hub assembly in a disc drive.
A typical disc drive includes one or more magnetic discs mounted for rotation on a hub or spindle. Where more than one magnetic disc is used, the discs are spaced apart from one another axially along the hub by spacers mounted between the discs. Conventional hubs typically include a flange portion which extends from one of the axial ends of the hub. The discs and spacers are placed concentrically about the hub and supported by the flange portion of the hub. The plurality of magnetic discs and the spacers are clamped down onto the flange portion of the hub using a clamp which is placed on the axial end of the hub, opposite the flange. Thus, the discs and spacers are all clamped to the hub for rotation with the hub about an axis of rotation generally defined by the radial center of the hub.
A typical magnetic disc drive also includes a transducer supported by a hydrodynamic air bearing which flies above each magnetic disc. The transducer and the hydrodynamic air bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive system based on commands received from the host system. The drive controller controls the disc drive to retrieve information form the magnetic discs and to store information on the magnetic discs.
An electromechanical actuator operates within a negative feedback, closed-loop servo system. The actuator moves the data head radially over the disc surface for track seek operations and holds the transducer directly over a track on the disc surface for track following operations.
Information is typically stored on the magnetic discs by providing a write signal to the data head to encode flux reversals on the surface of the magnetic disc representing the data to be stored. In retrieving data from the disc, the drive controller controls the electromechanical actuator so that the data head flies above the magnetic disc, sensing the flux reversals on the magnetic disc, and generating a read signal based on those flux reversals. The read signal is then decoded by the drive controller to recover the data represented by flux reversals stored on the magnetic disc, and consequently represented in the read signal provided by the data head.
As industry pressure requires disc drives to be reduced in size, the axial height of the stack assembly, and consequently the axial height of the entire disc file, becomes critical. In past systems, the clamp used to hold the discs about the hub was located above and screwed onto the hub with screws running in the axial direction. However, since the axial height of the stack assembly has become critical, the clamp and the screws used to fasten the clamp to the hub take up an undesirable amount of axial space.
Therefore, a heat shrink clamp was developed. Such a clamp is described in greater detail in U.S. Pat. No. 4,639,802. Such clamps typically include a clamp ring which has an inner diameter that is slightly smaller than the outer diameter of one axial end of the hub. The clamp ring is responsive to thermal energy and expands when thermal energy is applied to it and contracts when thermal energy is removed from it. Therefore, to assemble the clamp ring onto the hub, the clamp ring is first heated, thereby expanding it such that the inner diameter of the clamp ring is slightly larger than the outer diameter of the hub. The clamp ring is then placed about the hub and allowed to cool to establish a frictional or interference fit with the outer surface of the hub.
Just prior to placing the clamp on the hub, the plurality of discs and spacers are arranged about the hub and subjected to an axial load (referred to as the "preload"). The clamp ring is then put in place and allowed to form its frictional fit before the preload is removed. The clamp ring retains a portion of the preload and thus clamps the spacers and the magnetic discs to the flange located at the second axial end of the hub.
A prior disc spacer for use with a heat shrink clamp is described in the Brooks et al. U.S. Pat. No. 5,006,942. The disc spacer in Brooks et al. is a generally cylindrical ring with an annular groove in its outer cylindrical surface. The annular groove in the disc spacer makes the disc spacer somewhat compliant under the preload. Thus, after the preload is applied, and the thermally responsive clamp is placed on the hub and allowed to form an interference fit with the hub, a portion of the preload applied to the hub assembly is retained due to the compliance of the spacer. Consequently, the thermally responsive clamp secures the magnetic disc to the flange on the hub thereby securing the disc for rotation with the hub.
Two major deficiencies are present in the Brooks et al. design as applied to small disc drives with thin hub flanges and clamps. Application of the load to the outer diameter of the clamp and flange causes deflection of those components distorting the outer discs. Also, when the spacers compress, the contact point is variable depending on part tolerances. This also contributes to disc distortion.